It's an oft-repeated maxim that one of the reasons that Windows operating systems are plagued by so many viruses, worms, and security exploits is because they are so popular. Extrapolating on this, many have remarked that if Linux, MacOS, or other OSes become more popular, they will attract the attention of virus writers. That may be true, but the increased attention will not necessarily yield the same quantity of viruses and other exploits, says a Register article. Update: Rebuttal article.

"So, in Linux, as long as you've got email addresses in any of the files in your /home directory and permission to access the SMTP port, the viruses will run just fine. "

By default, a user must have root priveledges to access all ports under 1024, SMTP is port 25.

It should be clear that WorknMan is referring to the ability to the ability to make outgoing TCP connections on port 25 in order to create a mass mailer worm, which is something any user on the system can do.